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By its name, we can make out that an urban area is a city while a rural area is outside a city. The light from the sun reaches both the areas equally. The difference is that the temperature in urban areas is high and the temperature in rural areas is low.
This is purely dependent on the absorption and retention of heat by the surfaces of both the areas as per their environment. Rural areas are mostly filled with plants and are greener in general than the urban areas.
On the other hand, urban areas are less green and there is more infrastructure. Urban areas have big buildings, parking lots, sidewalks, etc. These things do not have the ability of acting as air conditioners like plants do. Hence, urban areas are easily heated.
This unusual state of the urban area is known as an Urban Heat island. Urban Heat Islands are noticed mainly in the peak winter season and the peak summer season. Also, when the hotter temperature in an urban area is highly noticeable due to extreme heat.
Causes of Urban Heat Island
1. Climate Change
Humans have been exploiting the environment which has a huge role in the climate change. There are extreme heatwaves in urban areas which contribute to the formation of Urban Heat island.
Plus, due to the urban heat island, there are further changes in the climate which will not have good results in the longer run.
2. Lack of Vegetation
Greenery in an area provides it shade and the air around it is cooler due to evapotranspiration. There are areas that are dominated by paved surfaces because of which there is less space for plants and trees.
In urban areas, the forests are getting entirely eliminated to fulfil housing demands and provide facilities to the people living there.
On beaches there is less greenery so the area is less cooler. As you may notice, the much desired suntan can easily turn into sunburn if the skin is exposed to sun long enough!
On the other hand, trees cool the environment through using solar heat and absorbing the carbon dioxide for their own food. As the plants and trees are being destructed, urban areas are getting hotter.
3. Low Albedo Materials
Albedo is referred to as the ratio of reflected solar energy. It is dependent on the arrangement of surfaces, materials, pavements, coatings, etc.
Albedo is a primary source of the formation of the microclimate.
Moreover, Albedo of a city varies. It depends on the surface arrangements such as orientation, pavements, etc. If the albedo of the urban surface is low, there will be more stored energy and it will be shown as an increase in temperature.
4. Excessive Use of Air Conditioners
Air conditioners are used worldwide as they are seen upon as a source of comfort. Air conditioners work on keeping the inside room cool through taking the heat of inside and releasing it outside. Hence, the outdoor temperature increases.
Moreover, air conditioning units for residential, commercial, office and industrial use are mainly located in Urban Areas. This contributes to temperature rise in the affected area.
5. Air Pollutants
Air pollution is a very big problem in the urban areas. Because there are many sources of air pollution in a city, the air of the air is the worst to breathe in.
There are gases that are released from vehicles, industrial pollutants that are released in the atmosphere, trap solar radiation.
These gases increase the temperature of the atmosphere and the microclimate effect becomes stronger and is harmful to the environment.
Events and gatherings happen more often in Urban than in the suburbs. This is mainly due to the convenient availability of many facilities. Carbon dioxide emission is in a huge volume in these areas.
Carbon dioxide absorbs and hold heat, which causes a rise in the atmospheric temperature. As an ultimate effect, it aids in the formation of heat island to a great extent.
Effects of Urban Heat Island
1. Increased Energy Consumption
Demand for air conditioners multiplies as temperatures rise in the city. Many studies reveal that the need for air conditioners increases by 1-2% every year, even more so in downtown.
As a result, these air conditioners give off more heat into the atmosphere.
Let me give an example to explain it better.
Imagine the temperature currently is 100°F (hottest month in Arizona).
You turn on the air conditioner and cool down your room. But you see…. so is your neighbor and thousand others in the town.
So when all of these air conditioners throw out warm air into the environment, the town starts warming up. This in turn makes your air conditioner work harder – and so on makes a snowball effect.
This leads to high electricity use.
In many cities, due to the extensive electricity use by air conditioners, there are power outages.
The gases used in air conditioners are also related to ozone layer depletion!
2. Elevated greenhouse gas emissions and air pollution
As discussed before, Urban Heat Island increases electricity consumption. The increased consumption means that the power plants have to work extra and operate more; these power plants require more fossil fuels to work.
The consumption of fossil fuels creates more air pollutants and greenhouse gases.
The leading greenhouse gases include carbon dioxide, nitrogen oxide, and carbon monoxide. These gases result in climate change and global warming, making the air more polluted.
3. Poses a danger to aquatic systems
The rise in temperatures causes elevated temperatures for pavements and rooftops. The heated rooftops cause increase in temperature of storm water runoff.
This heated storm water flows into the drainage system and raises the water temperatures of streams, rivers, lakes and oceans causing thermal pollution.
The aquatic system is affected by thermal pollution, especially the metabolism and reproduction of marine species, which can be very harmful to aquatic life.
4. Discomfort and danger to human health
The high rise in the temperatures is an outcome of an urban heat island, which affects human health.
As Urban Heat Island reduces the nighttime cooling, human health is negatively impacted due to exhaustion, discomfort, respiratory problems, heart strokes, headaches, and heat craps.
5. Secondary impact on weather and climate
Urban Heat Island can bring many other changes in the climate and weather other than high temperatures. It can affect the wind patterns, precipitation rates, formation of fog, and humidity.
The extra heat generated contributes to more intense wind movement that can stimulate precipitation and thunderstorm activity. These changes can also damage the plants that are growing.
6. Impacts on Animals
Urban heat island also affects animals. Many animals require a specific range of temperature to thrive, utilize, and colonize in the ecosystem they belong to.
When the temperatures get high, the environment gets harsh and unwelcome for these species and limit their activities such as breeding, reproduction, and metabolism.
The warm temperatures of urban cities might attract many animals to head towards the town, as they might be more suitable for survival.
Solutions to Urban Heat Island
1. Use of white and light-coloured concrete roofs
According to many studies, light-coloured and white roofs effectively reflect up to 50% more light and cuts down the ambient temperature. This has proven to be one of the best solutions to reduce the effects of Urban Heat Island.
Dark colours tend to absorb the heat, causing the surfaces to be warm. The use of white paint can also help to reduce the demand for air conditioners.
2. Green roofs and vegetation cover
A green roof is an excellent method. It is a practice to plant vegetation on the top, just like in a garden. During summers, plants prove themselves to be a very effective insulator.
They even keep the air cold, subsequently, less demand for air conditioners. Plants also help to reduce carbon dioxide from the air and produce fresh air.
3. Planting trees in cities
Planting trees on the outskirts of the city and in the town reduce the urban heat island effect and help to reflect solar radiation at the same time.
Trees have tons of benefits for the city!
For example, Trees absorb carbon dioxide and release oxygen in the air. The canopy provides the much-needed shade.
4. Green parking lots
Green parking lots use green infrastructure strategies, similar to green roofs. It cushions the elevation of high temperatures.
They even reduce storm water runoff, which can reduce the danger imposed on aquatic systems.
5. Implementation of heat reduction policies and rules
There should be the implementation of environmental laws and policies such as the Clean Air Act. This can also be done by creating more awareness among people by educating them.
Example of an Urban Heat Island in the United States
Intense heatwave in Oklahoma City
Oklahoma City is the largest city in the United States. A study was conducted to collect the data of the heatwave event. The study was based on two data sets, one from 15 July, and the other was from 15 August 2008.
The data was collected from the Oklahoma City Micronet and 10 Oklahoma Mesonet sites. Many stations were made to collect the data in both areas.
By looking at the data that the proper intensity of the heat was seen during the day between urban and suburban areas, the temperature values also increased.
The metropolitan areas’ temperature was 1 degree to 2 degrees warmer in the day and around 3 degrees warmer at night compared with rural areas.